1. Field of the Invention
This invention relates to optical systems for deflecting an image and, more particularly, to optical systems in which the image is deflected by decentering a portion of the entire system.
2. Description of the Related Art
When the photographer is shooting picture frames while walking, or riding on a vehicle such as car, aircraft, etc., the photographic lens is vibrated to displace the actual picture frame from the intended line of sight. This displacement increases as the focal length of the photographic lens increases.
There have been previous proposals for stabilizing the optical system against such accidental displacements in, for example, Japanese Patent Publications Nos. Sho 56-34847, 57-7414 and 57-7416.
In these documents, an optical member which constitutes part of the photographic system is arranged to be stationary relative to the line of sight against vibrations. By utilizing a prism this optical member and the other part generate oscillations when the vibration is introduced, and the image at the focal plane is deflected to obtain a stationary image at the focal plane.
Besides this, it is known to employ an acceleration sensor incorporated in the camera for detecting the vibratory motion or the jiggle. Its output is twice integrated to determine the momentum. Depending on the thus-obtained signal, an actuator moves a portion of the photographic system in a direction perpendicular to the optical axis to obtain a stationary image at the focal plane. As the actuator use can be made of, for example, a meter or a laminated assembly of piezoelectric elements arranged to oscillate in two dimensions independently of each other.
In general, the use of the method of oscillating a portion of the photographic system or a lens unit in compensating for the displacement leads to a prerequisite that the responsiveness of the operating mechanism therefore is sufficiently fast.
To this end, it has been required that the size and weight of the movable lens group for displacement compensation be as small as possible, that the inertial mass be reduced, that the relationship of the amount of movement of the compensation lens group with the resultant image shift in the focal plane be simplified, and that the time necessary to compute the required image shift from the angular deviation of the camera from a line of sight be shortened.
In addition thereto, the photographic lens has to be designed so that when decentered by moving the displacement compensator in a direction perpendicular to the optical axis, the optical performance is little lowered.
However, it is usually very difficult to obtain a photographic lens that fulfills all the above-described requirements. Particularly in the case of the displacement compensator having some refractive power, there was a drawback that when decentering took place, the grade of imagery was largely lowered, making it impossible to obtain pictures of good quality.
For note, the method of shifting the image in the focal plane by decentering a constituent lens unit of the lens system is exemplified in U.S. patent application Ser. No. 896,639.